There is a severe vulnerability in the widely deployed BIND DNS software that can allow an attacker to force a remote server to freeze and stop processing requests. The bug is in several recent versions of the BIND software.
BIND is a very popular DNS package that’s maintained by the Internet Systems Consortium and is probably the most widely deployed DNS software in the world. The ISC warned in an advisory this week that the vulnerability should be considered a high risk and that organizations running BIND 9.7.1 or 9.7.2 should update their systems right away to BIND 9.7.3.
“When an authoritative server processes a successful IXFR transfer or a
dynamic update, there is a small window of time during which the
IXFR/update coupled with a query may cause a deadlock to occur. This
deadlock will cause the server to stop processing all requests. A high
query rate and/or a high update rate will increase the probability of
this condition,” the ISC advisory said.
The group said that organizations running the vulnerable versions should either install BIND 9.7.3 or deploy one of the suggested workarounds, depending upon the needs of the organization.
“ISC was not able to reproduce this defect in 9.7.2 using -n1, which
causes named to use only one worker thread, thus avoiding the deadlock.
If your server is powerful enough to serve your data with a single
processor, this option may be fast to implement until you have time to
perform an upgrade,” the advisory said.
BIND (Berkeley Internet Name Domain) is a free and open-source name-server implementation and it is used in organizations around the world. The current production version is 9.7.3, which is not vulnerable to the DoS bug, and 9.8.0rc1, a release candidate for the next version, also is available. It’s not vulnerable to this bug either.